1. Field of the Invention
The present invention relates to a BPS receiver, and more particularly, to a BPS receiver which can receive simultaneously RF signal of different frequency band and process the RF signal received, minimize aliasing generated by RF signal.
2. Description of the Related Art
When a receiving unit converts a RF signal of a transmitting unit to a digital signal, if a receiver processes a RF signal according to a conventional sampling theory, the receiver should sample a RF signal with using double sampling rate for a carrier wave frequency(fc) of a RF signal.
The sampling rate increases simultaneously as the frequency of a RF signal increase. But, conventionally a real signal exists in 0.003%-0.2% of a modulated signal (RF signal) by a carrier wave frequency(fc). When a signal is modulated by a carrier wave frequency of high frequency, a receiver should sample a RF signal by higher sampling rate, sampled data's amount increase exponentially. Therefore, a receiver performs inefficiently process of data.
In order to solve the problem, a band pass sampling can sample a RF signal with using sampling rate which is lower than Nyquist rate of a RF signal.
The band pass sampling performs a sampling with using sampling rate which is lower than Nyquist rate. Therefore, data's amount generated by a sampling of a RF signal decreases. The band pass sampling is a Harmonic sampling or a Sub sampling, uses sampling frequency which is lower than Nyquist rate, a result of the use generates purposely aliasing. Hence the band pass sampling has an advantage that sampling rate basically depends on a data's bandwidth.
The band pass sampling is usually applied to a digital direct conversion or a RF direct conversion. When a band pass sampling is applied to a digital direct conversion, because the a band pass sampling directly performs a sampling after amplifying a RF signal received through a antenna in LNA, a wireless receiver of low-price and small-size may be embodied.
FIG. 1 illustrates a structure of a typical digital direct conversion receiver.
The typical digital direct conversion receiver will hereinafter be described with reference to FIG. 1.
An integer-position signal may be down-converted by 1st-order BPS (Band Pass Sampling) of minimum sample rate 2B.
A non-integer-position signal may be down-converted by 1st-order BPS (Band Pass Sampling) of fs>2B sample rate, but a sampling frequency fs may vary according to the position of a signal bandwidth.
Therefore a sample rate may vary according to a bandwidth and the position of band for universal access, hence a bandwidth of a RF filter may be varied.
A 2nd-order BPS (Band Pass Sampling) performs a signal process and a result of the performance removes aliasing, after sampling with using two analog-digital converter(ADC) having relative time delay. Therefore, a sample rate may be selected without considering aliasing, a minimum sampling frequency may be selected with the same as a bandwidth of a signal.
FIG. 2 illustrates a block diagram of a 2nd-order BPS receiver.
The typical 2nd-order BPS receiver will hereinafter be described with reference to FIG. 2.
When a bandwidth of an input steam is B, a sample rate for a RF signal is B. At this time, the aliasing for a RF signal is generated.
The latest paper discloses that sample is performed by delay time of τB=−2(n+1)TΔ when a data locates in Integer position, hence a response of a digital filter isn't affected, a digital embody of interpolant is possible.
The other side, CR(cognitive Radio) or SR(Smart Radio) uses a spectrum sensing for effective use of a frequency. The spectrum sensing is used for searching the other frequency for data communication while performing data communication through one frequency. Therefore, the 1st-order BPS or 2nd-order BPS described by FIG. 1 and FIG. 2 have difficulty for simultaneously receiving and processing two frequency, hence the 1st-order BPS or 2nd-order BPS have difficulty for application to CR or SR.
Besides, the object of the FIG. 1's 1st-order BPS receiver and the FIG. 2's 2nd-order BPS receiver is down-conversion of one RF signal. When more than one RF signal is simultaneously received and processed, a first RF signal is received by the receiver illustrated in FIG. 1 or FIG. 2, but if a second RF signal isn't located in special frequency band, aliasing may generate. In other word, a conventional digital direct conversion (BPS) receiver has a defect occurring aliasing while simultaneously receiving a plurality of RF signals.